Presence servers are known in the art. Such servers receive and maintain presence information regarding entities, such as computer or cell phone users, and provide presence information about the entities to subscribers. Accordingly, presence servers receive requests from publishing entities to publish presence information, as well as subscription requests from subscribing entities wishing to receive the published presence information.
Publishing entities are logical sources of information, such as an individual. The individual may have a cell phone and a personal computer, both of which are capable of providing presence information regarding the same individual at the same time. The presence information from the cell phone may differ or even conflict with the presence information from the personal computer. Other sources of presence information for an individual include, for example, telephones, mobile devices, personal devices and laptop computers. A presence server combines the presence information received from these disparate sources in order to create a single consistent view of the status of the publishing entity (i.e. the individual).
FIG. 1, to which reference is now made, illustrates the manner in which a typical presence server 120 processes incoming presence information from publishing entities 30 and provides notification services to their associated subscribing entities 35. Publishing entities 30 “publish” presence information by sending it to presence server 120. Subscribing entities 35 “subscribe” to specific publishing entities 30 by sending requests to presence server 120.
Presence server 120 comprises an aggregator 122. Aggregator 122 aggregates presence information received from publishing entities 30, and uses it to compose a presence information document 160 for each of publishing entities 30. Presence server 120 sends copies of these presence information documents 160 to each subscribing entity 35 associated with the specific publishing entity for which each document 160 was composed.